In the preparation of magnetic recording materials, such as for use in magnetic recording disks, it is common practice to use magnetic particles such as .gamma.-Fe.sub.2 O.sub.3, dispersed in a binder mixture such as an epoxy/phenolic resin. This mixture of magnetic particles and binder is typically applied to a disk substrate as a liquid/solid dispersion, such as by spin coating, and the resultant coating is then cured in air to convert the liquid coating to a firm magnetic layer. However, when these types of magnetic compositions are cured in air, a coercivity lower than desired is often produced.
It is believed to be that when air curing a magnetic composition as discussed above, there is added anisotropy due to the chemical reduction of to Fe.sup.3+ to Fe.sup.2+ at the surface of the particles. It is well known that at elevated temperatures Fe.sup.3+ ions will react with many functional groups (e.g., alcohols, phenols). The organics become oxidized while the Fe.sup.3+ ion is reduced to Fe.sup.2+. The Fe.sup.2+ ion is then reoxidized to Fe.sup.3+ by oxygen (or oxygen-related species) trapped at the surface of the particles. The oxygen is then replaced by oxygen from the surrounding atmosphere. Catalysis literature commonly discusses this cycle for transition metal ions. This is similar to the more widely known oxygen uptake by chromic acid solutions. Essentially, the .gamma.-Fe.sub.2 O.sub.3 is an oxidation catalyst for the epoxy-phenolic system in the normal air-cure.